Modern aircraft cockpits comprise a display system comprising several display screens. The information displayed is controlled and modified by means of various human-machine interfaces. The trackball constitutes one of its interfaces. It mainly comprises a rolling ball whose upper part is accessible to the user. The lower part rests on motion sensors which can be of different types and which detect the rotations of the ball in two right-angled directions. The information from the sensors makes it possible to displace a graphical cursor on a display screen.
In an aeronautical application, the rolling ball is subjected, during certain flight phases, to vibrations or accelerations which can be high. Also, it cannot be allowed to rotate freely. It must be braked to prevent any spurious motion during these critical phases. This adjustment is difficult in as much as the ball has to be braked sufficiently so as not to be sensitive to the vibrations but the rotation must remain flexible enough for a user to be able to rotate the ball without significant force.
Currently, the adjustment of the brake is ensured by a setup represented in FIG. 1. A ring 2 comprising a flexible seal 3 is fixed to the body 4 of the device which comprises the rolling ball 1. This ring surrounds the upper part of the rolling ball. The braking force of the flexible seal is ensured by shims 5 arranged between the lower part of the ring 2 and the body 4. It is symbolized by the two inclined white arrows of FIG. 1. This solution has two drawbacks. It is complex to implement. Moreover, in operation, the braking forces gradually increase. This hardening is due to a clogging of the various mechanical elements such as the axes, the rings, the rolling bearings, associated with intensive use on an aeroplane. Ultimately, the rolling ball must be removed, dismantled and cleaned.